1. Field of the Invention
The present invention relates to a rotary joint support structure which performs a center-thru coolant feed operation and a spindle of a machine tool and electric motor which are provided with such a rotary joint support structure.
2. Description of the Related Art
In a machine tool, to improve the machining precision of a workpiece and extend the tool life, a coolant is run through a bore formed in a spindle etc. up to the machining point so as to cool the machining point in a “center-thru coolant” feed operation. In the spindle etc. which is carried at a machine tool in which a center-thru coolant feed operation is performed, to increase the speed of the spindle and improve the reliability, the general practice has been to use a detachable outside support type rotary joint to feed high pressure coolant.
A detachable outside support type rotary joint includes a rotating part which rotates together with the spindle etc. and a stationary part which is attached to the housing. When coolant flows through such a rotary joint, it passes between the seal part of the rotating part and the seal part of the stationary part. These seal parts can separate from each other, so the coolant sometimes leaks out from between the rotating part and the stationary part.
Therefore, in Japanese registered Patent No. 2966799, a drain hole or cutaway part for draining the coolant which leaked out from the rotary joint is formed in the support housing. Due to this, the leaked coolant is prevented from invading the inside of the spindle or electric motor. Further, Japanese Registered Patent No. 3806312 discloses to feed air to a drain hole so that leaked coolant does not remain inside the drain hole.